This invention relates to a method and apparatus for cementing a production conduit within an underground arcuate bore drilled along an arcuate path between two surface locations, such as disclosed in our copending application Ser. No. 853,344 filed Apr. 17, 1986, now U.S. Pat. No. 4,679,637.
Copending application Ser. No. 853,344, the entire disclosure of which is incorporated by this reference, describes an apparatus and method for drilling in one direction of travel a pilot bore hole along an underground arcuate path between two earth surface locations, and then enlarging in an opposite direction of travel the initial pilot bore hole for receiving a production conduit therein. A conventional drill pipe string is utilized in drilling the initial bore hole and the drill string may have a spud bit on its leading end for thrusting the drill string along a predetermined arcuate path to form an initial pilot bore hole of a relative small diameter, such as around five (5) inches in diameter for example. As an alternative, a rotary drill bit may be provided on the leading end of a drill string with an in-hole hydraulic motor for rotating the drill bit such as might be desirable when relatively hard formations are encountered. After the drilling of the initial pilot bore hole and exit of the drill string from the exit surface opening, the drill bit on the end of the drill string is removed and a reamer is connected to the drill string at the exit end for pulling back through the hole for enlarging the pilot bore hole to the desired diameter for the production conduit. The production conduit is pulled into the hole trailing the reamer, either in the initial reaming step or in a separate step after the enlargement of the pilot bore hole by the reamer. An annulus is formed about the production conduit of a thickness around two (2) to six (6) inches, for example, dependent on the diameter of the production conduit and the type of formation encountered. For example, the enlarged opening may be around thirty (30) inches in diameter for a production conduit of twenty (20) inches in diameter, such as a pipeline, thereby providing an annulus between the pipeline and the adjacent surface defining the enlarged opening having a thickness of five (5) inches. Heretofore, cementing methods have been utilized in vertical drilling for cementing the annulus between the outside of the casing in the vertical bore hole and the wall of the hole, or to seal between inner and outer casing strings. The cement has normally been pumped down the hole into the annulus and has been effective to seal the casing within the bore hole. Various types of plugs have been provided within the inner casing or drill string to divert the cement outwardly into the annulus.